11:33 -- The circular ring is connected to a constant voltage (V+), so it's at AC ground. It prevents signals in other parts of the circuit from affecting the voltage of the disc inside the ring. (It's a "guard ring".) The transistor's collector (C) is connected to this ring / AC ground. The disc inside the ring is connected to the transistor's base (B). The S-shaped piece of PCB that's connected to the transistor's emitter (E) is a section of transmission line, which resonates at a particular frequency and which determines the circuit's frequency of oscillation. Since one end of the S-shaped piece of PCB is connected to the transistor's emitter (E), which is the signal source, and since the other end of the S-shaped piece of PCB is connected to capacitors which are connected to ground (so that the far end of the S-shaped strip is at AC ground), then the S-shaped strip is a 1/4 wavelength resonant section of transmission line. There is feedback between transistor's base (B) and its emitter (E) through the space between the short strip of PCB ("stub") that's connected to B and the section of the S-shaped piece of PCB that's connected to E. The size of the space between that stub and the S-shaped piece of PCB that's connected to E largely determines the degree of coupling (feedback) between the transistor's base and emitter. The longer the space or the narrower the space, the greater the coupling / feedback. So the circuit is a one transistor oscillator (specifically, a grounded-collector oscillator), having a resonant circuit that's connected to the transistor's emitter, and having some coupling / feedback between its emitter and base.

Not an effin clue, but Big Clive's enthusiastic detective work draws you in and you keep watching.

This will be perfect for catching that ghost that keeps turning on my soldering iron after I turned it off.

Appreciate these videos so much - truly, truly good quality educational content that is often impossible to find. Keep on keepin' on!

This is a awesome talk on rf doppler detectors, the bit in the beginning which covers the oscillator and how one can modulate the amplitude is gold. Love it, thanks Clive!

Just rig a microwave oven to run with the door open, if you smell pork, you have detected a body 😂😂

It’s amazing how such a simple circuit happens to be so complex. Thanks for breaking it down for us Clive, it’s much appreciated!

Loved this video! The fact that you tried to comprehend the magic of RF and still put out this video - the transparent film screen showing the back was a great way for you to explain of your thought train in a very slick way!. Always look forward to your new content, I’m pretty sure I’ve watched all your back catalogue :-D

Hehe, I also made those “simple” (slightly illegal) FM transmitters when I was young, most often with a preceding microphone amplifier, to become a small bugging device. Often choosing close to 88MHz or 108MHz, and then any ordinary FM-radio (preferably small and hand held) could be used as receivers. I learned then, that there was a big complexity to RF-electronics, since I put a lot of effort in doing very nice and clean builds, with often no good results, while a class mate made a very “ugly” build (blobby soldering, wires not cut close to the PCB etc) and that worked better than any of the rest of the class mates. It’s fantastic that a simple circuit like that actually ends up as a FM-transmitter. The simplicity to build things like this for FM an AM, together with the avast amount of existing equipment, is actually why I feel a bit “scared” that DAB will “destroy” the possibilities for future young kids, interested in electronics, to test and learn in an exiting (slightly illegal) way. Of course you can do a lot of MUCH cooler things today, with all sorts of micro controllers and advanced chips, sensors etc, but not at the same low level. I’m glad Sweden postponed the switch to DAB. It really feels meaningless, since you could get the digital feeds via mobile data streams and the cost to switch all existing analog equipment would be enormous. It have played out it’s role... Keep at least some of the current FM-band analog (as well as the AM-band) as a backup system and for the kids to play with ;) Btw, we soldered the antenna (normally measured to a quarter to the wavelength) to one of the loops of the wounded inductor.

The Concentric Circles thing is the actual Antenna Element Back Plane . The Squiggle Line Track simply a Load Inductor doubling as the Antenna. If you measure the Distance between the Squiggle Track folding back on it's self you will find it a fraction of the actual operating frequency in .wavelength.. Probably 1/8th or 1/4 wavelength.

If Clive says it's complex it's really complex. Another really interesting video Clive thanks for all the hard work you put into these. Glad I stumbled on your channel many moons ago, it fascinates me how all these things work and makes me want to get into making a few projects myself

You’re just an incredibly brilliant dude. Old videos and new, I’m always blown away.

Thanks for doing the hard work. I ordered a bunch of these several months ago and plugged one in. It works! I just never got around to a tear-down.

As 50+ old fart it's been 30 years since I've thought about 1/(2pi*sqrt(LC)). You're video made my brain work - thank you.

Amazing explanation and homework.. Especially because of the super zoomed PCB picture that was used. I'm sure it helped the viewers understand the PCB a lot more easily. Keep up the good work.

This reminds me of a gadget I built before touch sensors existed. I used a PIC to generate PWM into a coil, which coupled with another coil. Somehow I could measure the phase between coils, which I put through an op-amp and back into the PIC. The theory was that my finger would change the phase. They laughed at me, said it can't work, but it did! I put two of these in a box and by sliding my finger up and down on the surface, I controlled a PWM fluorescent dimmer. Happy memories. My goal was to make a water-proof switch.

Clive, as a 50+ y/o electronics and radio enthusiast, may I say, if your video's were available when I was doing my training, I would be "up there" now, I really enjoy all your "tear-downs" and the way you detail your explanations. They come across so well. Even something like this complex uWave circuit. Well done.... You're a top bloke!

I was a broadcast engineer for a couple of decades, but RF was never my strong suit. I could keep big transmitters running, but I was way more comfortable with studio gear and computer stuff. I totally understand what you're saying!

Hi Bigclive - really interesting video - I remember UHF/Microwave construction being described to me in the late 1970s as a bit like "plumbing" - the usual headache when designing higher and higher frequency circuits was trying to overcome and eliminate stray capacitance, but as you get towards the top end, they stop being a "problem" and start becoming an "enabler" - but you instinctively realise that :) What's more interesting to see is that (compared to the tolerances within microchip fabrication) the relatively crude technology behind copper etching can be used to great effect. It's a bit like looking at plans for a fairly crude valve amplifier and realising that the "cleverness" is all down to the physical construction, which we've all kind of forgotten with the ability to cram more and more components into an ever decreasing space to overcome design flaws This is a perfect example of less being very much more :)

This break-down caused me to realize that not every part of a circuit is either positive or negative relative to a connected part; but rather, the relationship can be more complicated; time-based or based on detection/externalities.

I love these relatively long videos, it's a lazy Saturday afternoon, wife is having a nap with the little one and I can just veg and watch you explain cool stuff. Some of your previous videos have given me great ideas for work projects too (Rpi/arduino stuff), so cheers for that too!

your large format pcbs are a brilliant display tool. What an excellent presentation.

I bought two of these intending to use them as some sort of alarm, (instead of the LED you have) but did not do anything with them. Now I understand what's going on and can proceed further. Thanks a lot for doing this video and also thanks for the many knowledgeable comments from everyone.

Where is the Signal Path god when you need him...

Great work Clive..these videos generate thought, conversation and new ideas..keep them coming. Gary in USA

I think you are correct with the screening you spoke of. Back in my army days that screen was made of copper components and used to tune the device to see it's target.

Clive I think this was the best one yet.

To paraphrase the late great Arthur C Clarke, microwave technology is indistinguishable from magic.

It may actually be more interesting watching Clive when he doesn't know exactly what's going on than when he does.

Perfect timing, I just took delivery of 10 of these microwave detectors and haven't opened them yet! Cheers

Thanks for this. I bought a dash cam hardwire kit which is apparently a movement detector and it's so light I thought it was fake. All it had was one of these circuit boards. I now see that a tiny circuit is all it takes to make a microwave transmitter!

EXCELLENT Video BigClive, once again you bring us mere mortals outstanding, interesting and simply awe-striking photo overlays with sublime PCB Exploded views, thank you immensely

Thank you Clive, a very intriguing, detailed explanation. It is fair to say that I need to watch this many more times before any information permeates into my brain (and is retained). Thank you again; you help me enjoy learning (slowly).

I was trying to figure out how the circiuts work (and they do very well!). Your video was the best and honest video I found! I highly (!) appreciate all the effort and time you have put into making this video, althought english is not my first language and I do not undestand every piece!

5:20 "The ZTX300 was also one." Instant flash back to Analogue Electronics in Higher Physics, 1986-7, where we had a tray of components and the transistors were ZTX300 and ZTX500.

Clive, thank you for teaching me about this device, I've had one in the drawer for quite awhile now. I think i will temper with it's C-TM with resistor and maybe short it out. What i really wanted from this device was the magnitude or perhaps frequency of detection and not so much staying on for a duration.

Always fun to see what other engineers work with, very interesting.

I love RF circuits , thank you Bigclive

I bought some of these for a prank on my boss (we are in an office prank war... he started it... lol) and I wanted to know how it worked. Eventually I decided I’ll never know and that all I needed to know is that it did work. Fast forward 2 months and here I am watching Clive on an 8 month old video on the chips I bought. I have been a fan for two years, and somehow this is the one video I missed. Haha, thank you for this closure!

Many years ago as i mooched around the local library I noiticed that a book enttled 'The Deadly Fuze' never moved. Eventually curiosity got the better of me and I took it out.Turned out to be the story of the development of the WW2 Proximity Fuze. Built into shells and fired up the barrel of a gun! And this was in the days of valves!! Can't remember the operating frequency but acorn valves could get up to about 500Meg. Used in anti aircraft shells and ordinary artillery shells. And now we've got shells with GPS built in!!!

I have a bunch of these and they are great, but I never bothered to try to figure them out, I didn't do very well in my RF and wireless classes when getting my degree. I understood diversity and multipathing, QAM and PSK, but for actually how circuitry worked and a lot of the math involved, not a chance. That stuff is black magic, to the people that really know it, much respect.

I was on the development team of the C&K/Honeywell DT-7xx k-band Dual Tec microwave/pir motion detectors back in Y2K. I did a lot of GTEM work for rfi and international certifications and UL listing. That round pad pad on the with the positive ring could be adding a few pf capacitance to keep rf noise out of the transistor. RF can be funky at gigahertz frequencies. I watch your videos to jog my memory. My kung fu is old and haven't touched an oscope or frequency analyzer since 2004 working on Pave Paws. That was SLBM rocket science ;)

Fascinating..Ive just bought an outside floodlight with microwave sensor from CPC, havnt put it up yet and wondered how it worked compared to PIR ..Thanks Clive :)

If you ever get interested, I'd love to hear your explanation of mass spectrometers and the quadropole mass selector. They're all about how alternating electric fields interact with ions of different masses.

The feedback from the collector to the base is in the transistor, mainly the internal capacitance between the collector and emitter. The square trace connected to the base is less an inductor/capacitor and more a delay line. The oscillator operates as a common base amplifier. The "squiggly" emitter line is a delay line. The disk of copper on the bottom behind the transistor is simply a ground plane. Some capacitance is there but it's unintentional. The ring of copper is the actual antenna. The ring and the disk ground plane act like a fresnel lens and makes the radar output more like a dipole antenna. When you move towards or away from the antenna, not only do you cause a doppler shift but you mainly case the frequency to shift (you're now part of the tuned circuit. At cm waves both are pretty much the same thing). The wiggly part of the emitter track introduces a delay from the frequency a few pico seconds ago and mixes it with the frequency that's happening now. In phase oscillations use less current than out of phase oscillations. The increased current drain for an out of phase signal is dropped and filtered by the emitter resistor (which is where the real feedback and transmit occurs) and the associated emitter/ground capacitors for detection.

Great work Clive. Embedding these in a timber staircase to identify individual steps. Then to trigger LED lighting.

I'm grateful that they broke out the 3.3v supply as well - used this in a project recently. Had no idea that the RF part was basically black magic.

Did anyone else notice how Clive drew his own face in this video? - Just look back at the part where he draws the diagram of the P.I.R. sensor at the top of the sheet.... Now, tell me that's not a self portrait! Thanks, Clive, for another truly enthralling video on something I know absolutely nothing about. - Give me valves (tubes) and high voltages any day. But, we shall learn........

Thanks Clive, excellent video and much appreciated

I really like this one, Clive. Thanks.

Clive it’s a good job I love the sound of your voice because despite really trying I didn’t understand a f*cking thing tonight. Thanks for posting anyway though I really appreciate the hard work you put in to educate the masses.

I have some ceiling lamps I bought from Costco that I'm sure have this technology in them. I love when the light goes on when I enter a hallway. For the first 2 months, we all said thank you to the light every time.

I made these when I was kid too. I can remember my mother nearly feel off her chair when she heard me on the radio

Very nice video and exploration of this interesting module ! Greetings from Holland

that usb power bank is "DIRTY", cant even imagine what i thought it was when i first saw it.

I ask for this when u went live that day thank you mate

A hybrid coupler in ring configuration ("rat race coupler") perhaps. These couplers typically have four ports. Power input at port 1 splits and travels both ways round the ring. At ports 2 and 3 the signal arrives in phase and at port 4 it's out of phase and cancels. The reflected, out of phase signal (from your body) can be made to "unbalance" the ring which effectively brings one port to a higher potential than the other ports. Those eclipsed portions of ring might be the port couplings. Just a guess- I am not a µwave engineer (but have played with transmission lines in the past).

Back in electronics school, my teacher had been a elec tech for radios in fighter jets. He told the story of a jet that would have radio troubles. After some time of trying to figure it out,, the E7 boss man, handed him a can of polish, and told him to polish the inside of the box the radio sat in... It seems that the box was a capacitor in the circuit. ... hmmm Well, the polishing worked,,, at least that is what we were told... Thanks and keep up the good work.

Imagine all the time and research going into the design only to have it copied by the Chinese and sold for 70 cents a module.

I used to make a very similar VHF transmitter circuit, using a varicap diode to alter the frequency for FM modulation. Range about quarter of a mile. I think I used a BC108 transistor. The capacitor across the coil was a variable trimmer type.

I at one time worked on 45w 850mHz transmitters at the factory. I would tune the circuits be adding or removing silver solder from the copper patterns on the board. They were very sensitive to anything being moved around the power transistors.

I used to make those FM-band transmitters too-- circa 1967. In those days we could buy "Poly-Paks" transistors, basically floor-sweepings. But they were perfectly usable 2N706's, 3 for $1. You could put a crystal microphone onto the base and pick up the signal and sounds for a dozen feet or more. Fun times. It was legal in the USA at power levels up to 50 milliwatts and 3 feet of antenna. You have some base-emitter feedback there.

Well you did a fine job splaining it, I was lost but then caught up. Flooded kansas again. Rain for the last 5 days. Supposed to be sunny tomorrow. Cheers.

A collaboration with the Signal Path is called for.

I think of things like this as engineers taking physics and breaking its back over their knee. In ten years it will probably be taught to 14 year-olds and be considered just normal everyday stuff. I love watching the way technology, behind the scenes, is advancing with quiet, almost, unnoticed, steps. Thank Clive for the excellent video.

i just did a thing of which i am inordinately proud. i bought a bunch of these, and decided 3 secs was too brief for the output signal. so i found the data sheet, learned to solder 0603 smd bits, removed the 10nf timing cap, popped a 100nf one in it's stead, and voila! it now switches for 30 seconds...and for my next trick, i just ordered some arduino nano PCBs and all the bits on the BOM. i am only going to try and make my own 'arts and crafts' arduino nano! and a mere year ago i was horrified by the thought of even soldering the headers on one. i learned it all from watching YT vids.

6:20 pirate radio was such a cool thing...I’m sure a lot of smaller pirate stations used similar designs!

That was quite interesting indeed. Great video.

I think this is a voltage controlled oscillator, it doesn’t use a fixed frequency. As others have said, the circular elements on the back plane are part of the antenna. For this sort of circuit to work the antenna needs to have an outrageously high Q, and ideally a pretty low radiation resistance, which a loop antenna provides. Essentially the ring looks to be a loop antenna acting mostly as a receive antenna. It’s coupled to to the transmit antenna with a sort of hybrid between a gamma match and a Patterson loop style capacitive network. The 1k resistor and the two adjacent capacitors right before the sense input are an RC pi filter tuned to the oscillator’s stable frequency. When the environment around the sensor changes, the amount of reflected power and the phase of the received signal changes slightly, which causes a change in the circulating current in the receive loop, which causes the complex impedance on the oscillator output to change, which changes the oscillator’s frequency. The frequency change means the signal will move relative to the pass band on the RC pi network, changing the attenuation of the signal and altering the voltage at the sense pin, and the chip just triggers on the change. If you have an RTL-SDR dongle or similar you should be able to confirm this by watching the signal in the waterfall. I bet it swings like mad when you sweep your hand near the sensor. Clive, if you don’t have an SDR handy, I’ll order a couple and put it on the spectrum analyzer, and I’ll also send you a little SDR dongle. Super handy little gadgets for poking at RF circuits like this.

With a high enough operating frequency a circuits behavior becomes indistinguishable from MAGIC.

I've used them as movement sensors in a few motion activated arduino systems. One thing of note (apologies if others have already said this) is they seem to work on detecting motion of fluids (bearing in mind the human body is mostly water). You can prove this by first waving an empty water bottle in front of it, then waving a full water bottle.

Very interesting video, thanks Clive

I feel like I should be getting course credit for this. Very nice video!

Pretty clever. You really gotta stare at it to see all the layers. The single transistor is being used for several things at once. The base is capacitively balanced between the TX and RX in such a way that if they don't cancel each others opposing capacitance charge the difference will change the bias of the transistor. A lot like how a phase lock loop can demodulate FM. It's seems a lot like just a microwave frequency version of a phase lock loop metal detector that's been cleverly manipulated out of a single transistor and some passives. The metal detector doesn't beep unless you swing it, but in this case the coils are stationary and the metal moves. The higher the frequency the more the water in the soil reflects back on a metal detector. That's why they only use around 7khz.

Awesome video my friend! I also have 5 of those unit and I did add a cds on the board....and the range went down but a lot my unit has about 1 meter range now. Thanks for explaining those little pad! Cheer from Canada!

The oscillator circuit is probably common collector. The feedback is from the emitter to the base through a transformer to get the required amplitude increase. Since the collector is grounded, the collector to base capacitance becomes part of the tank circuit and the Miller effect is eliminated. The transistor can then operate at the highest possible frequency.

The mode which always resets before triggering again is useful when you're doing the on/off timing externally. This way the external circuit can continously detect movement.

Hey Clive, what an interesting circuit. And what you call a `cheap and tacky' meter has been my main meter for about 15 years, so reliable. LOL

The ring is a resonator at wavelength equal to its circumference. The top of the ring is pinned firmly to VCC by those bypass capacitors forcing that to be an E field node and the bottom to be an anti-node. The collector and emitter have opposite phase so that the meander line couples to the resonator on the back. Do those two vias on the disk connect to the base? They seem to be about -120/240 degrees away from the top standing wave node. Combined with the transistor characteristics and the base capacitor overlap, I predict this brings the positive feedback into phase with the resonator. Any Doppler effect shift will be f0 (v/c). That disk might couple to reflected energy so that the same transistor mixes those two signals with the 1k -- 1 nF forming the LPF to reject the carrier and sum frequencies.

Thanks Clive I was going to use this in place of PIR sensors in my outdoor woodland thing.( Bluestone, Wales). Methinks I'll stick with the PIRs for that. Interesting possibilities concerning the various "missing" resistors though. Clever, and cheap, device.

I was impressed I have ordered 10 from Ali, @31 pence each, it's crazy that you can buy something so clever for so little.

I can remember TV engineers talking about waveform. Your mention of the curved edges reminds me of that. Billions of cycles per second don't care for corners. :-D

That blue battery usb suply make me think of another divice :-), Thumps upp as always.

That RF oscillator could be used as the volume oscillator in a theremin. It would be interesting to attach an oscilloscope to the 'sense' point and see how sensitive it is. I might buy some of these and try to build a theremin.

at first I thought the circle on the back was a ground but yes I agree BigClive, it's some sort of resonator making virtual capacitors across the base, collector, emitter

so damn handy, thanks a bunch! I've always wanted to tune these things

Clive - I finally figured out what you meant. I can use the 3.3VDC Hi circuit to close the ground loop for the camera's dry input. It took me a month. I feel slightly dumb. :)

I'm using one of those microwave sensors as an under-monitor movement sensor. It is used to switch on an LED strip under my monitor when movement is sensed. The problem I have with these is that the sensing is patchy. They can often see me over the room (and through a wall) but will often not detect when I'm sitting at the keyboard (2ft away) moving my hands about the keyboard and to mouse etc (1ft away). My current solution is to have one under the monitor looking at me and another blu-tac-ed under the wooden desk and mousepad. I've never yet worked out the front/back of the sensor to find the most sensitive side. I've been tempted to try a PIR sensor on the monitor instead but never got around to trying yet.

A fair amount of that went over my head, as the actress said to the bishop!

Love your videos, keep up the good work 😀😀😀👍

Hi Clive, enjoyed the video as always...I've played with these for a while and perhaps the most interesting benefit you may have missed? Because they are microwave you can mount them behind doors/wood etc and detect motion the other side...try putting it under your desk (assuming no it's not metal) and moving your hand above. It will trigger...so making a detector than can be hidden behind wood or plasterboard may have applications in home security etc. Keep up the good work. Ps...if you mount it above the desk and move our hand below you may go blind!

Clive’s got it right he could be an Electrical Engineer... As my intro to EE professor said the difference between science and engineering is that engineers estimate, like Clive and his capacitor values being feasible, and scientists require exact values meaning they’re not as flexible dealing with real life components’ tolerances.

Some motion detectors used in security/burglar systems use both a PIR and a microwave detector (called "dual-tech" in North America at least). Both sensors have to detect/trip in order for the zone to be considered violated, which greatly reduces false alarms.

Im only a low level entry into RF circuits but I am aware in microwave frequencies an antenna called a discone is used most common. They tend to use a capacitive 'hat' and obviously get smaller the higher the frequency, so I think you have a very squashed discone antenna with all the relevant coupling components. The idea with RF is you want as much power thrown out as possible without any RF reflecting back down the feed to the transmitter or damage will occur. I know its very critical with high power outputs, but not so sure with very low power like this but it could have an effect if not controlled properly. It is called a discone because that is exactly what it looks like, a disc on a cone with an insulated separator between them. The disc is fed with RF and the cone is the ground reference and the size and angle relationship ( radius of disc and angle/length of cone with solid cone and disc or using rods as a cone and disc ) between them determines the frequency you want to transmit at. As mentioned by another commenter further down the receive parameters of the antenna will usually be compromised by a fraction of the desired transmit frequency ie 1/2 wave, 1/4, 1/8, 3/8 etc are typical because of size limitations on the board or your available space at home because the actual size required for a 1:1 transmitter in most cases would be far greater than the space available. Reception through an antenna does not need to bother so much with sizes of things as all it does is alter the amount of energy/noise/interference available to be received. In short, the antenna length/size must be a fraction of the wavelength of the frequency you wish to transmit at and the load on the transmitter device should be as close to 50 ohms as possible to prevent a dead short, because transmitting RF is almost a dead short and a lot of energy is at the transmitter in commercial antennas which is why you should never EVER touch a live transmitting element as you WILL get burned lol. With an AM/MW antenna the entire pole is live, ShortWave uses very long wires across towers and FM uses lots of types from yagis, log periodic, ground plane X shapes, monopoles, discones, dipole etc.. Basically the higher the frequency, the shorter/smaller the antenna length. Interestingly, behind those small to massive "snare drum shaped" microwave transmitters you see everywhere is just either a small discone, bowtie or dipole element in the center. The drum is just a reflector for line of site comms. :) Probably got some bits wrong but didnt want this to go on forever.. which it has lol

thanks for detailed explanation

excellent video! Thanks for sharing

Great to watch you second guess what and how the designer was trying to achieve. There must be a bit of detective Columbo in your DNA. One more thing....

OMG! ZTX300 series transistors ... from Ferranti, where I worked as a computer engineer back between 1976 and 1979! Used LOTS of ZTXxxx series transistors and still have.many spares. As ubiquitous as the BC107,8,9s and later BC149 types! Or the US equiv of the 2N2222!

I'm wondering what the smallest object is that this could detect? The chip obviously does some thresholding but the output from opamp 2 (pin 12) could be very interesting for those looking for very small changes. I am thinking of small mammal detection very close to the sensor.

The reason I'm pursuing electronics, can't wait 'till you hit 1mill Clive yas mate.